Liquid composition, ink jet recording method, ink jet recording apparatus and recorded image

ABSTRACT

The invention provides an aqueous liquid composition containing a water-soluble monomer, a photopolymerization initiator and an aqueous medium and further containing a polymer emulsion, wherein the water-soluble monomer is a monomer that has two or more ethylenically unsaturated bonds and is curable with an active energy ray.

This application is a divisional of U.S. patent application Ser. No.13/793,671, filed Mar. 11, 2013, pending, which is a divisional of U.S.patent application Ser. No. 12/887,998, filed Sep. 22, 2010, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid composition, an ink jetrecording method, ink jet recording apparatus and a recorded image.

2. Description of the Related Art

An ink jet recorded image, in particular, a recorded image formed withan aqueous ink involves a problem on fastness properties such as waterfastness and scratch resistance. As measures to solve this problem, ithas been known in recent years to use an ink jet ink containing anemulsion.

On the other hand, as a technique for forming a fast image, is mentioneda technique of using an aqueous liquid composition containing awater-insoluble polymer present in a state of an emulsion. When thewater-insoluble polymer present in the state of the emulsion in theliquid composition (hereinafter also referred to as a polymer emulsion)is applied to a recording medium, the polymer emulsion aggregates toform a film as the water around the emulsion decreases. The film formedcan protect an image formed on the recording medium to improve thefastness of the image.

However, the above-described technique has caused the following problemsin some cases. The polymer held in the state of the emulsion in anaqueous medium has caused in some cases destruction of the emulsionstructure due to storage under a severe environment (high temperature,vibration), long-term storage or an influence by the pH of a coloringmaterial upon addition of the coloring material into the liquidcomposition to cause deposition of polymer components. When the liquidcomposition containing the polymer emulsion has been applied to arecording medium, in some cases, the filming (aggregation) of thepolymer emulsion has rapidly progressed to make the film formed uneven,and consequently the quality of the resulting image has becomeinsufficient, and the fastness has not been sufficiently improved.

In order to solve this problem, in an aqueous ink using an emulsion, itis known to add an aid for inhibiting the rapid progress of filming ofthe emulsion to improve the uniformity of a film formed by the emulsion.As such aids are generally used plasticizers and high-boiling alcoholicsolvents. However, such an aid is liable to remain in a film formed, andconsequently the fastness of the film may not be improved in some cases.On the other hand, in recent years, there has been a dramatically strongdemand for diversity to meet individual needs of customers and necessityfor high image quality in an image forming technique.

Specific techniques for forming an image with a liquid compositioncontaining an emulsion include a technique described in WO01/057145.WO01/057145 describes a technique for improving the fastness of an imagewith a liquid composition containing acroylmorpholine.

SUMMARY OF THE INVENTION

However, the above-described prior art has involved the followingproblem. Specifically, according to the investigation by the presentinventors, the stability of the liquid composition, and the uniformityand strength of a film have not been sufficiently achieved according tothe technique disclosed in WO01/057145 in some cases.

Accordingly, it is an object of the present invention to provide anaqueous liquid composition curable by irradiation of active energy rays,also suitably usable as an ink containing a coloring material, excellentin stability, and capable of forming a uniform film and imparting highfastness to an image. Another object of the present invention is toprovide an ink jet recording method and an ink jet recording apparatususing the liquid composition, and a recorded image.

The above objects are achieved by the present invention described below.According to the present invention, there is thus provided an aqueousliquid composition comprising a water-soluble monomer, aphotopolymerization initiator and an aqueous medium and furthercomprising a polymer emulsion, wherein the water-soluble monomer is amonomer that has two or more ethylenically unsaturated bonds and iscurable with an active energy ray. According to the present invention,there are also provided an ink jet recording method and an ink jetrecording apparatus using the liquid composition, and a recorded imageformed by the ink jet recording method.

According to the present invention, there is provided an aqueous liquidcomposition curable by irradiation of active energy rays, also suitablyusable as an ink containing a coloring material, excellent in stability,and capable of forming a uniform film and imparting high fastness to animage. According to the present invention, there are also provided anink jet recording method and an ink jet recording apparatus using theliquid composition, and a recorded image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments.

DESCRIPTION OF THE EMBODIMENTS

The present invention will hereinafter be described in detail bypreferred embodiments. The present inventors have carried outinvestigations. As a result, it has been found that an aqueous liquidcomposition containing a polymer emulsion and a water-soluble monomerthat has two or more ethylenically unsaturated bonds and is curable withan active energy ray is excellent in the following respects, thusleading to completion of the present invention. More specifically, theliquid composition can form a uniform film on an image obtained byirradiation of active energy rays, is excellent in fastness such as thecrosslinking degree of a cured product of the water-soluble monomer andadhesion between the cured product and a film formed by the polymeremulsion and also satisfies the level of low viscosity required in inkjet recording applications. In addition, the liquid composition isexcellent in long-term storage stability and ejection stability (alsoreferred to as stability merely) required in aqueous liquid compositionsin particular.

The reason why the liquid composition according to the presentinvention, which contains the above-described specific water-solublemonomer, can form a uniform film and achieves excellent results incuring performance and stability is not clearly known. However, thepresent inventors speculate as follows. First, the mechanism with whichthe uniform film can be formed by using the liquid composition accordingto the present invention is presumed to be as follows. The monomer usedin the present invention has a hydroxyl group or an ethylene oxide groupand thus exhibits specific water-solubility (hydrophilicity).Accordingly, the water-soluble monomer can hold water in the liquidcomposition like a high-boiling alcoholic solvent. In addition, thewater-soluble monomer can gradually release the water held uponformation of a film formed by the polymer emulsion, so that it issupposed that the monomer can function as an ideal aid agent to inhibitthe rapid aggregation of the polymer emulsion so as to gradually form afilm.

Then, the mechanism with which the curing performance of the liquidcomposition according to the present invention is improved is presumedto be as follows. The water-soluble monomer used in the presentinvention is cured in a film formed by the emulsion upon irradiation ofactive energy rays unlike a conventional aid agent liable to remain in aliquid state in the film, so that the fastness of the film obtained fromthe emulsion can be improved. In other words, the water-soluble monomercan form the film together with the polymer emulsion, so that anextremely fast film can be formed compared with the case where thewater-soluble monomer alone or the polymer emulsion alone is used.

The action and effect in aqueous ink jet recording that is a principalapplication example of the liquid composition according to the presentinvention will hereinafter be described. Incidentally, as the activeenergy ray used in the present invention, may be used ultraviolet raysor electron rays. Description is given below taking a liquid compositionof such a type that radical polymerization take place by ultravioletrays to be cured, as a typical example. However, the application rangeof the present invention is not limited by this example at all.

The liquid composition according to the present invention can exhibit aparticularly marked effect on a recording medium which has liquidabsorbability but is hard to improve the color of a pigment and scratchresistance, such as plain paper. However, in the present invention, arecording medium with low liquid absorbability of the aqueous liquidcomposition or a non-absorbent recording medium made of a metal orplastic may also be used.

The respective components of the active energy ray curable liquidcomposition according to the present invention, which has such excellentaction and effect as described above, will now be described.

Polymer Emulsion

The liquid composition according to the present invention contains apolymer emulsion. In the present invention, the polymer emulsion means awater-insoluble polymer present in a state of an emulsion in the liquidcomposition. Incidentally, the water-insoluble polymer means a polymerhaving a solubility of 1% by mass or less in water under normalconditions (ordinary temperature, ordinary pressure, ordinary humidity).The polymer emulsion used in the present invention is favorably made upby a thermoplastic resin capable of forming a film. The weight averagemolecular weight (Mw) of the polymer is favorably within a range of5,000 or more and 10,000 or less.

No particular limitation is imposed on a monomer usable for obtainingthe polymer emulsion according to the present invention. However, thefollowing monomer may be suitably used. Specific examples thereofinclude styrene, acrylic esters such as methyl acrylate and ethylacrylate, vinyl chloride, vinyl acetate, acrylic acid, and methacrylicacid.

The average particle size of the polymer emulsion is favorably within arange of 0.01 μm or more and 2 μm or more. In the present invention, theaverage particle size of the polymer emulsion can be determined bymeasuring its d50 particle diameter that is a median diameter by meansof a laser light scattering type particle size measuring apparatus.

The polymer making up the polymer emulsion is favorably a polymer of astructure having a plurality of groups polymerizable by irradiation ofactive energy rays. As the polymer emulsion according to the presentinvention, may also be used a commercially available polymer emulsion.Examples of the commercially available polymer emulsion include VINYBLAN277 (emulsion of a vinyl chloride-acrylic ester copolymer, availablefrom Nisshin Chemical Industries Co., Ltd.), JONCRYL 537J (emulsion of astyrene-acrylic acid copolymer, available from BASF Japan Ltd.) andUCECOAT 7655 (polymer emulsion having a plurality of groupspolymerizable by irradiation of active energy rays, available fromDAICEL-CYTEC COMPANY LTD.).

The polymer emulsion used in the present invention is favorablycontained in a content range of 1.0% by mass or more and 40.0% by massor less based on the total mass of the liquid composition.

Water-Soluble Monomer

The monomer used in the present invention is water-soluble. Thewater-solubility in the water-soluble monomer means that the monomer isdissolved in water in an amount of 5% by mass or more under normalconditions (ordinary temperature, ordinary pressure, ordinary humidity).Accordingly, the water-solubility in the present invention means theso-called hydrophilicity. When a monomer exhibits the hydrophilicity ofthis extent, it can be present stably in the aqueous liquid composition.

In the present invention, as the monomer exhibiting thewater-solubility, is favorably used a monomer having one or morehydroxyl groups. Although the detailed reason is not known, a firmerfilm can be formed compared with a case where a monomer achieving thewater-solubility by another group alone than the hydroxyl group, such asa monomer having an ethylene oxide group, is used when the monomerachieving the water-solubility by the hydroxyl group is used, so thathigher fastness can be imparted to the resulting image.

The water-soluble monomer used in the present invention is a monomerhaving two or more ethylenically unsaturated bonds in its structure andcurable with active energy rays. Examples of the monomer havingethylenically unsaturated bonds and curable with active energy raysinclude monomers having functional groups such as a (meth)acryl groupand a (meth)acrylamide group. The water-soluble monomer according to thepresent invention has two or more ethylenically unsaturated bonds andthus has two or more such functional groups as described above. Theliquid composition according to the present invention contains theabove-described specific water-soluble monomer and may further containany other monomer than this monomer.

In addition, the water-soluble monomer used in the present inventionfavorably has a molecular structure satisfying the relationship of thefollowing expression (1)3.5≦(Molecular weight of water-soluble monomer)/(28.05×(Number ofunsaturated double bonds in molecular structure))≦8.0.  Expression (1)

The expression (1) means the proportion of molecules making up theethylenically unsaturated bonds in the water-soluble monomer. Ingeneral, since a group making up an ethylenically unsaturated bond meansCR₁R₂═CR₃R₄ (R₁ to R₄ being arbitrary groups), it is difficult tocalculate the total molecular weight of molecules contributing to theethylenically unsaturated bond without considering the molecularstructure of each monomer. Thus, in the present invention, the lowestmolecular weight of the groups making up the ethylenically unsaturatedbond, i.e., the molecular weight (28.05) of ethylene, in which R₁ to R₄are all H, was used to calculate the proportion of molecules consideredto substantially contribute to the ethylenically unsaturated bonds inthe water-soluble monomer. According to the investigation by the presentinventors, the water-soluble monomer satisfies the relationship of theexpression (1), whereby the strength of the film cured can bestrengthened.

The water-soluble monomer according to the present invention may furtherhave any other functional group than the hydroxyl group, the ethyleneoxide group and the group having the unsaturated double bond in itsstructure. Specific examples of such a functional group include acarboxyl group, a sulfonic group, a phosphoric group, an amino group andsalts thereof, an amide group, an amide linkage group, an ester linkagegroup, and a sulfone linkage group.

The molecular weight of the water-soluble monomer according to thepresent invention is favorably within a range of 200 or more and 2,000or less. As described above, the water-soluble monomer according to thepresent invention is dissolved in water in an amount of 5% by mass ormore, and is more favorably dissolved in an amount of 20% by mass ormore.

As described above, it is satisfactory for the water-soluble monomerused in the present invention to have 2 or more ethylenicallyunsaturated bonds. Since a faster film can be formed as the number ofthe ethylenically unsaturated bonds increases, no particular limitationis imposed on the upper limit of the number thereof. However, sincethere is a tendency for the viscosity of the liquid composition toincrease as the number of the ethylenically unsaturated bonds in thewater-soluble monomer increases, the number of the ethylenicallyunsaturated bonds is favorably 2 to 6. The number of the ethylenicallyunsaturated bonds in the water-soluble monomer is more favorably 3 or 4.

Exemplified Compounds 1 to 9 that are particularly favorable specificexamples of the water-soluble monomer used in the present invention areshown below. Needless to say, the scope of the present invention is notlimited thereto.

[Specific Examples of Water-Soluble Monomer]

A synthesis process for the water-soluble monomer used in the presentinvention is not limited at all, and any conventionally known processmay be used. As an example, the synthesis process of an amide compoundas described above is described in, for example, Japanese PatentApplication Laid-Open No. 2007-119449. The synthetic process of anN-vinylamide compound as described above is described in, for example,Japanese Patent Application Laid-Open Nos. H08-81428 and 2002-167369. Inaddition to the exemplified compounds the structures of which have beenshown above and the amide compounds the synthesis processes of whichhave been shown, commercially available compounds may also be used.

In the present invention, the content of the water-soluble monomer inthe liquid composition is favorably 1.0% by mass or more and 40.0% bymass or less based on the total mass of the liquid composition. The massratio between the polymer emulsion and the water-soluble monomer, whichare used in combination in the liquid composition in the presentinvention, is favorably within a range of from 5:1 to 1:10. When themass ratio is controlled within this range, both of the glossiness ofthe film and the fastness of the film can be achieved extremelysuitably.

Photopolymerization Initiator

The photopolymerization initiator used in the present invention isfavorably a hydrophilic photopolymerization initiator and is alsofavorably a compound which generates a radical by active energy rays.The photopolymerization initiator is further favorably an initiatorgenerating a radical upon using ultraviolet rays as the active energyrays. Specific examples of the hydrophilic photopolymerization initiatorsatisfying these favorable conditions include compounds represented bythe following general formulae (1) to (5).

In the general formula (1), R₁₅ is an alkyl group having 1 to 5 carbonatoms or a phenyl group, with the proviso that the phenyl group may beunsubstituted or mono- to tetra-substituted by any substituent selectedfrom halogen atoms, alkyl groups having 1 to 5 carbon atoms, alkyloxygroups having 1 to 5 carbon atoms, a sulfonic group, a carboxyl group, ahydroxyl group and salts thereof; —SO₃ ⁻M⁺, —CO₂ ⁻M⁺, —O⁻M⁺, and thefollowing atomic group (E), R₁₆ is an alkyloxy group having 1 to 5carbon atoms or a phenyl group, with the proviso that the phenyl groupmay be unsubstituted or mono- to tetra-substituted by any substituentselected from halogen atoms, alkyl groups having 1 to 5 carbon atoms andalkyloxy groups having 1 to 5 carbon atoms, and R₁₇ is the followingatomic group (E).

Atomic Group (E)

In the atomic group (E), R₁₈ is —[CH₂]_(x2)— (x₂ being 0 or 1) or anunsubstituted or substituted phenylene group, R₁₉ is a hydrogen atom, ora sulfonic group, a carboxyl group, a hydroxyl group or a salt thereof;or —SO₃ ⁻M⁺, —CO₂ ⁻M⁺or —O⁻M⁺, k is an integer of 0 to 10, and 1 is 0or 1. In the general formula (1) and the atomic group (E), M⁺ ions are,independently of one another, a hydrogen ion, alkali metal ion oralkaline earth metal ion, or an ammonium ion represented by HNR₂₀R₂₁R₂₂(R₂₀, R₂₁ and R₂₂ being, independently of one another, a hydrogen atom,an alkyl group having 1 to 5 carbon atoms, a monohydroxyl-substitutedalkyl group having 1 to 5 carbon atoms or a monohydroxyl-substitutedphenyl group).

In the general formula (2), m3 is an integer of 1 or more, n3 is aninteger of 0 or more, and m3+n3 is an integer of 1 to 8.

In the general formula (3), R₂₃ and R₂₄ are, independently of eachother, a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, andm4 is an integer of 5 to 10.

In the general formula (4), R₂₆ and R₂₇ are, independently of eachother, a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R₂₅is —(CH₂)_(x)— (x being 0 or 1), —O—(CH₂)_(y)— (y being 1 or 2) or aphenylene group, and M is a hydrogen atom or an alkali metal.

In the general formula (5), R₂₈ and R₂₉ are, independently of eachother, a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, andM is a hydrogen atom or an alkali metal.

In the general formula (1), the alkyl group or phenyl group of R₁₅ andthe phenylene group of R₁₈ may have a substituent. Specific examples ofsuch a substituent include halogen atoms, alkyl group having 1 to 5carbon atoms, alkyloxy groups having 1 to 5 carbon atoms, groupsrepresented by the atomic group (E), a sulfonic group, a carboxyl group,a hydroxyl group, and salts of the sulfonic, carboxyl and hydroxylgroups (—SO₃M, —CO₂M and —OM). R₁₅ is particularly favorably a phenylgroup having an alkyl group having 1 to 5 carbon atoms as a substituent.Ms are, independently of one another, a hydrogen atom, an alkali metal,an alkaline earth metal or an ammonium represented by HNR₃₀R₃₁R₃₂ (R₃₀,R₃₁ and R₃₂ being, independently of one another, a hydrogen atom, analkyl group having 1 to 5 carbon atoms, a monohydroxyl-substituted alkylgroup having 1 to 5 carbon atoms or a monohydroxyl-substituted phenylgroup).

Examples of the salt of R₁₅ in the general formula (1) include —SO₃M,—CO₂M and —OM. The Ms are, independently of one another, a hydrogenatom, an alkali metal, an alkaline earth metal or an ammoniumrepresented by HNR₃₃R₃₄R₃₅ (R₃₃, R₃₄ and R₃₅ being, independently of oneanother, a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, amonohydroxyl-substituted alkyl group having 1 to 5 carbon atoms or amonohydroxyl-substituted phenyl group).

The alkyloxy group or phenyl group of R₁₆ in the general formula (1) mayhave a substituent, and examples of the substituent include halogenatoms, alkyl groups having 1 to 5 carbon atoms and alkyloxy groupshaving 1 to 5 carbon atoms. R₁₆ is particularly favorably an alkyloxygroup, and —OC₂H₅ or —OC(CH₃)₃ is favorable.

The alkyl groups of R₂₃, R₂₄, and R₂₆ to R₂₉ in the general formulae (3)to (5) may have a substituent. Specific examples of such a substituentinclude halogen atoms, a sulfonic group, a carboxyl group, a hydroxylgroup and salts of the sulfonic, carboxyl and hydroxyl groups (—SO₃M,—CO₂M and —OM). The Ms are, independently of one another, a hydrogenatom, an alkali metal, an alkaline earth metal or an ammoniumrepresented by HNR₃₆R₃₇R₃₈ (R₃₆, R₃₇ and R₃₈ being, independently of oneanother, a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, amonohydroxyl-substituted alkyl group having 1 to 5 carbon atoms or amonohydroxyl-substituted phenyl group).

Among these compounds, a water-soluble acylphosphine oxide representedby the general formula (1) is favorable. More specifically, thefollowing Exemplified Compound A is favorably used as thephotopolymerization initiator. As a synthetic process for the followingExemplified Compound A, may be suitably used the process described inJapanese Patent Application Laid-Open No. 2005-307199.

When a thioxanthone type hydrophilic photopolymerization initiator isused as the hydrophilic photopolymerization initiator in the presentinvention, a hydrogen donor is favorably added. Example of the hydrogendonor usable in the present invention include triethanolamine andmonoethanolamine.

In the present invention, 2 or more photopolymerization initiators maybe used in combination. The use of 2 or more photopolymerizationinitiators can expect that light having a wavelength which cannot beeffectively utilized with one photopolymerization initiator is used tomore accelerate the generation of the radical so as to improve thecuring characteristics.

Aqueous Medium

The liquid composition according to the present invention contains anaqueous medium. In the present invention, water is favorably used as theaqueous medium. A mixed solvent of water and a water-soluble organicsolvent is more favorably used as the aqueous medium. The water-solubleorganic solvent is particularly favorably one that is water-soluble andcan satisfy ink jet characteristics such as ejection stability, and allconventionally known organic solvent may be applied. However, the mixedsolvent contains water in an amount of favorably 50% by mass or more,more favorably 90% by mass or more, based on the total mass of the mixedsolvent from the viewpoints of influence on the environment and odorupon work.

Examples of water-soluble organic solvents usable in the presentinvention include glycol ethers such as ethylene glycol monomethylether, ethylene glycol monoethyl ether, ethylene glycol monoisopropylether, ethylene glycol monoallyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, triethylene glycol monomethylether, triethylene glycol monoethyl ether, propylene glycol monomethylether and dipropylene glycol monomethyl ether; polyhydric alcohols suchas glycerol, and water-soluble amide compounds such as 2-pyrrolidone.Since the water-soluble organic solvent, in particular, ahighboiling-point water-soluble organic solvent, may be incorporated ina film formed in some cases to deteriorate the fastness of the resultingimage as described above, the content of the water-soluble organicsolvent is favorably less than 10.0% by mass based on the total mass ofthe liquid composition.

Liquid Composition Containing No Coloring Material

The active energy ray curable liquid composition according to thepresent invention may be used as being colorless without containing sucha coloring material as described below. When the liquid composition isprepared so as to have ink jet recording characteristics, it can beprovided as a transparent ink jet liquid composition of the activeenergy ray curing type. When such a liquid composition is used, a clearfilm can be obtained because the liquid composition contains no coloringmaterial. Examples of uses of the liquid composition containing nocoloring material include the following: an undercoat for impartingvarious suitabilities for image recording to a recording medium and anovercoat for the purpose of protecting the surface of an image formedwith an ordinary ink and imparting decoration and gloss. In the liquidcomposition of this type, a colorless pigment or fine particles, whichdo not intend to provide coloring, may also be dispersed and containedaccording to uses such as prevention of oxidation and prevention offading. The addition of them can improve various characteristics such asimage quality, fastness and handling property of the resulting recordedarticle in either the undercoat or the overcoat.

When the transparent liquid composition applicable to the above uses isprovided, the total amount of the polymer emulsion and water-solublemonomer is favorably 10.0% by mass or more and 70.0% by mass or lessbased on the total mass of the liquid composition. In addition, thephotopolymerization initiator is favorably contained in an amount of 1.0part by mass or more and 10.0 parts by mass or less per 100.0 parts bymass in total of the polymer emulsion and water-soluble monomer and inan amount of at least 0.5 parts by mass per 100.0 parts by mass of theliquid composition.

When the liquid composition according to the present invention is usedin a form of containing no coloring material, a polymerizablelow-viscosity monomer is favorably contained as a solvent therein. Theadvantage of the use of such a material, which is not an ordinarysolvent, resides in that influence on solid physical properties isreduced because such a material does not remain as a plasticizer in thesolid after the curing reaction by the active energy rays. Specificexamples of the polymerizable low-viscosity monomer includeacryloylmorpholine, acrylamide, methylenebisacrylamide, monoacrylates ofmonosaccharides, monoacrylates of oligoethylene oxides and monoacrylatesof dibasic acids.

When the liquid composition according to the present invention is usedin a form of containing no coloring material, it is favorable not to usean additive imparting moisturization as described below. The reason forit is that viscosity increase is small because a solid component such asa pigment is not contained, and some viscosity increase can be easilyrecovered if any. Needless to say, an additive having highermoisturization properties as described below may be added in a necessaryand minimum amount. Various kinds of additives such as a surfactant mayalso be added. These may be selected from many compounds commonly usedin aqueous ink jet liquids.

The case where the liquid composition according to the present inventionis used in a state (as an ink) that a coloring material is containedwill now be described. Such a liquid composition is hereinafter referredto as an ink.

Coloring Material or Pigment

The liquid composition according to the present invention may contain acoloring material such as a pigment in addition to the componentsdescribed above. In this case, a pigment dispersion obtained byuniformly dispersing a pigment in an aqueous medium is favorably used asthe coloring material. As the pigment dispersion, is favorably used apigment dispersion obtained by stably dispersing a pigment in water bythe action of an anionic group.

The average particle size of pigment particles is within a range offavorably 25 nm or more and 350 nm or less, more favorably 70 nm or moreand 200 nm or less. When the average particle size of the pigmentparticles is controlled within the above favorable range, the pigmentparticles can be made sufficiently smaller than the wavelength ofvisible rays to obtain a clear recorded image with less lightscattering. Incidentally, the average particle size of the pigmentparticles can be determined by measuring its d50 particle diameter thatis a median diameter by means of a laser light scattering type particlesize measuring apparatus.

When a pigment is contained as the coloring material, the concentrationof the pigment in the liquid composition is favorably 0.3% by mass ormore and 10.0% by mass or less based on the total mass of the ink. Whenthe concentration of the pigment is of the order of 0.3% by mass or moreand 1.0% by mass or less, the concentration is within such a range thatit is usable as a light-color ink though it varies according to thecoloring power of the pigment and the dispersed state of the pigmentparticles. When the concentration is higher than the above range, aconcentration used for a general color ink is given.

Coloring Material or Dye

In the ink according to the present invention, a conventionally knowndye may be used as the coloring material without limiting it to apigment as described above, and the ink can be provided as an inkcontaining a water-soluble dye in a dissolved state within such a rangethat no practical problem in fading caused by irradiation of activeenergy rays occurs. A coloring material dispersion containing a dispersedye or oil-soluble dye in a dispersed state may also be applied like thepigment dispersion. These dispersions may be suitably selected asnecessary for the end application intended.

The favorable content of the dye in the ink is within a range of 0.1% bymass or more and 10.0% by mass or less based on the total mass of theink. When the content of the dye is low, such an ink may be suitablyapplied to the so-called light-color ink.

Other Additives

When the liquid composition according to the present invention is usedas an ink containing a coloring material, various additives such aswater-soluble organic solvents and surfactants may be added into theink. The additives are used for the purpose of inhibiting the volatilityof the ink, lowering the viscosity of the ink and controlling wettingtendency with respect to a recording medium.

When the additives are added in an amount of 10.0% by mass or more intothe ink, the additive themselves may be incorporated in the film in somecases. Therefore, it is favorable to use a recording medium having highliquid absorbability and conduct natural or forced drying after the inkis cured with the active energy rays for inhibiting the lowering of thefilm strength by the additives. Incidentally, the monomer in the inkaccording to the present invention is water-soluble, and thus has highaffinity for water and certain moisturizability in itself. Therefore,the ink according to the present invention may not contain any additiveaccording to the composition thereof.

When a non-liquid-absorbent recording medium is used as the recordingmedium, the recording medium cannot be expected to have the ability toabsorb the additives. It is thus favorable to limit the amount of theadditives to a minimum. Specifically, the content of the additives isfavorably less than 10% by mass based on the total mass of the ink. Thecontent is more favorably less than 5% by mass. When the above-describedrecording medium is used, no additive is favorably added to the ink ifpossible.

When the liquid composition according to the present invention is usedas the ink containing the coloring material, examples of the additivessuitably used include such various glycol ethers and polyhydric alcoholssuch as glycerol as mentioned above as the water-soluble organicsolvents usable in the present invention.

When the liquid composition according to the present invention is usedas the ink containing the coloring material, the content of the aqueousmedium, the content of the photopolymerization initiator and the totalamount of the polymer emulsion and water-soluble monomer are favorablyadjusted according to the absorption property of the coloring material.Specifically, the content of the aqueous medium is favorably 40.0% bymass or more and 90.0% by mass or less, more favorably 60.0% by mass ormore and 75.0% by mass or less, based on the total mass of the liquidcomposition. The total amount of the polymer emulsion and water-solublemonomer in the liquid composition is favorably 1.0% by mass or more and35.0% by mass or less, more favorably 10.0% by mass or more and 25.0% bymass or less, based on the total mass of the liquid composition. Thecontent of the photopolymerization initiator is favorably 0.1% by massor more and 7.0% by mass or less, more favorably 0.3% by mass or moreand 5.0% by mass or less, based on the total mass of the liquidcomposition though it varies according to the total amount of thepolymer emulsion and the water-soluble monomer.

Ink Jet Recording Apparatus

In the present invention, an ink jet recording apparatus equipped with aunit for applying the liquid composition to a recording medium and aunit for irradiating the liquid composition applied to the recordingmedium with active energy rays may be favorably used. In the presentinvention, an apparatus in which an UV lamp is arranged on a front sideof a paper discharge section, paper feeding and discharging areconducted by winding a paper sheet on a roll, or a drying section isseparately provided may be suitably selected as the ink jet recordingapparatus.

In the present invention, an ultraviolet irradiation apparatus isfavorably used as an active energy ray irradiation unit. The ultravioletirradiation apparatus is favorably a mercury lamp with a vapor pressureof 1 Pa or more and 10 Pa or less during lighting. Since the emissionspectrum in an ultraviolet region of the mercury lamp is within a rangeof 450 nm or less, in particular, 184 nm or more and 450 nm or less, themercury lamp is suitable for efficiently reacting the polymer emulsionand water-soluble monomer contained in the liquid composition.Specifically, as the mercury lamp, may be suitably used a metal halidelamp, high pressure mercury lamp, extra-high pressure mercury lamp,xenon flash lamp, deep UV lamp, electrodeless UV lamp using microwavesor UV laser.

An ultraviolet irradiation apparatus using UV-LED of a light emittingdiode system or an UV excimer lamp may also be suitably used. Theultraviolet irradiation intensity of the ultraviolet irradiationapparatus such as the ultraviolet irradiation apparatus using UV-LED ofthe light emitting diode system or the UV excimer lamp is favorably 500mW/cm² or more and 5,000 mW/m² or less from the viewpoint ofpolymerization rate. If the ultraviolet irradiation intensity isinsufficient, the strength of the resulting film may not be sufficientlyachieved in some cases. If the irradiation intensity is too strong, arecording medium may be damaged, or the fading of a coloring materialmay occur in some cases.

The ink jet recording method according to the present invention has anejection step of ejecting the liquid composition on a recording mediumand a curing step of irradiating the recording medium on which theliquid composition has been applied with active energy rays to cure thewater-soluble monomer. The above-described ink jet recording apparatusis favorably used for performing the ink jet recording method accordingto the present invention.

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples. However, the presentinvention is not limited by these examples unless going beyond the gistof the present invention.

Examples 1 to 18 and Comparative Examples 1 to 9

The respective components shown in Tables 1-1 to 1-5 were mixed andthoroughly stirred. The resultant mixtures were then filtered underpressure through a filter having a pore size of 5 μm, thereby preparingactive energy ray curable aqueous liquid compositions according toExamples 1 to 18 and Comparative Examples 1 to 9. The structures ofExemplified Compounds 1, 5 to 9, and A used in the liquid compositionsof Examples in the Tables are as described above. The structures ofcomparative compounds in Table 1 are as described below. Incidentally,water was added in such an amount that the total amount of each liquidcomposition amounts to 100% by mass. Exemplified Compounds 1 and 5 to 9are water-soluble monomers having 2 or more ethylenically unsaturatedbonds. With respect to these compounds, the value of the expression (1)is shown in the parentheses.

TABLE 1-1 Composition of liquid composition (unit: % by mass) Example 12 3 4 5 6 Coloring Pigment dispersion 3.0 3.0 3.0 material (*1) (solidcontent) Polymer emulsion VINYBLAN 277 (*2) 10.0 10.0 (solid content)UCECOAT 7655 (*3) 10.0 10.0 10.0 10.0 Water-soluble Exemplified 10.010.0 10.0 10.0 polyfunctional Compound 1 (7.2) monomer Exemplified 10.010.0 Compound 5 (9.3) Comparative Compound 1 Comparative Compound 2Polymerization Exemplified 1.0 1.0 1.0 2.0 2.0 2.0 initiator Compound ASurfactant SN Wet 125 (*4) 0.1 0.1 0.1 0.1 0.1 0.1 Water solubleGlycerol organic solvent Water Bal. Bal. Bal. Bal. Bal. Bal.

TABLE 1-2 Composition of liquid composition (unit: % by mass) Example 78 9 10 11 12 Coloring material Pigment dispersion (solid content) (*1)Polymer emulsion VINYBLAN 277 (*2) 10.0 10.0 10.0 10.0 16.7 17.1 (solidcontent) UCECOAT 7655 (*3) Water-soluble JONCRYL 537J (*5)polyfunctional Exemplified 3.3 2.9 monomer Compound 1 (7.2)  ExemplifiedCompound 5 (9.3)  Exemplified 10.0 Compound 6 (7.61) Exemplified 10.0Compound 7 (3.57) Exemplified 10.0 Compound 8 (3.28) Exemplified 10.0Compound 9 (5.67) Comparative Compound 1 Comparative Compound 2Polymerization Exemplified 1.0 1.0 1.0 1.0 1.0 1.0 initiator Compound ASurfactant SN Wet 125 (*4) 0.1 0.1 0.1 0.1 0.1 0.1 Water-solubleGlycerol organic solvent Water Bal. Bal. Bal. Bal. Bal. Bal.

TABLE 1-3 Composition of liquid composition (unit: % by mass) Example 1314 15 16 17 18 Coloring material Pigment dispersion (solid content) (*1)Polymer emulsion VINYBLAN 277 (*2) 1.8 1.5 15.0 2.5 5.0 (solid content)UCECOAT 7655 (*3) Water-soluble JONCRYL 537J (*5) 10.0 polyfunctionalExemplified 18.2 18.5 5.0 17.5 15.0 10.0 monomer Compound 1 (7.2) Exemplified Compound 5 (9.3)  Exemplified Compound 6 (7.61) ExemplifiedCompound 7 (3.57) Exemplified Compound 8 (3.28) Exemplified Compound 9(5.67) Comparative Compound 1 Comparative Compound 2 PolymerizationExemplified 1.0 1.0 1.0 1.0 1.0 1.0 initiator Compound A Surfactant SNWet 125 (*4) 0.1 0.1 0.1 0.1 0.1 0.1 Water-soluble Glycerol organicsolvent Water Bal. Bal. Bal. Bal. Bal. Bal.

TABLE 1-4 Composition of liquid composition (unit: % by mass)Comparative Example 1 2 3 4 5 6 Coloring material Pigment dispersion 3.03.0 (solid content) (*1) Polymer VINYBLAN 277 (*2) 10.0 10.0 10.0emulsion (solid content) UCECOAT 7655 (*3) 10.0 10.0 10.0 Water-solubleExemplified polyfunctional Compound 1 (7.2) monomer Exemplified Compound5 (9.3) Comparative 10.0 10.0 Compound 1 Comparative 10.0 10.0 Compound2 Polymerization Exemplified 1.0 1.0 1.0 2.0 2.0 initiator Compound ASurfactant SN Wet 125 (*4) 0.1 0.1 0.1 0.1 0.1 Water-soluble Glycerol10.0 organic solvent Water Bal. Bal. Bal. Bal. Bal. Bal.

TABLE 1-5 Composition of liquid composition (unit: % by mass)Comparative Example 7 8 9 Coloring material Pigment dispersion (*1) 3.03.0 (solid content) Polymer emulsion VINYBLAN 277 (*2) 10.0 (solidcontent) UCECOAT 7655 (*3) 10.0 Water-soluble Exemplified polyfunctionalCompound 1 (7.2) monomer Exemplified 10.0 Compound 5 (9.3) ComparativeCompound 1 Comparative Compound 2 Polymerization Exemplified 2.0 1.0initiator Compound A Surfactant SN Wet 125 (*4) 0.1 0.1 Water-solubleGlycerol 10.0 organic solvent Water Bal. Bal. Bal.

(*1) The pigment dispersion was prepared in the following manner andused in such a manner that the solid content thereof is the value shownin Tables 1-1 to 1-5. C.I. Pigment Blue 15:3 was used as a pigment, anda styrene-acrylic acid/ethyl acrylate random copolymer (weight averagemolecular weight: 3,500, acid value: 150 mg KOH/g) was used as adispersant. These materials were dispersed by a bead mill to finallyobtain a cyan pigment dispersion having a pigment solid content of 10%by mass and a mass ratio of the pigment and the resin (P/B) of 3:1. Theaverage particle size of the pigment used was 120 nm. The averageparticle size of the pigment was determined by measuring its d50particle diameter that is a median diameter by means of Nanotrac 150(manufactured by Microtrac Inc.) that is a laser light scattering typeparticle size measuring apparatus.

(*2) Available from Nisshin Chemical Industries Co., Ltd.

(*3) Reactive polymer available from DAICEL-CYTEC COMPANY LTD.

(*4) Available from SAN NOPCO LTD.

(*5) Available from BASF Japan Ltd.

With respect to Exemplified Compounds 5, 7 and 8 and ComparativeCompounds 1 and 2, commercially available products were used as theyare. Exemplified Compound 6 was synthesized according to the followingprocess. Specifically, after ethylene oxide was added to diglycerol byan addition reaction, epichlorohydrin was further reacted to obtain aderivative of glycidyl ether. Thereafter, acrylic acid was added to theresultant derivative by an addition reaction to obtain Exemplifiedcompound 6. In addition, Exemplified Compound A was obtained byconducting synthesis according to the process described in SynthesisExample 1 of Japanese Patent Application Laid-Open No. 2005-307199.

Evaluation of Film Properties

Each of the liquid compositions having the respective compositions shownin Tables 1-1 to 1-5 was used to evaluate its film properties in thefollowing manner. First, each of the liquid compositions was ejected ona commercially available PET (polyethylene terephthalate) film from arecording head by means of BJF 9000 (manufactured by Canon Inc.) so asto give a coating amount of 10 g/m². Then, the thus-coated PET film wasimmediately subjected to an ultraviolet (UV) irradiation apparatus. Atthis time, an UV curability evaluation apparatus, Model LH6B(manufactured by FUSION UV Systems Inc.) was used as an electrodeless UVlamp using microwaves. The irradiation intensity was 5,000 mW/cm², andthe conveying speed was 0.4 m/sec. In order to show the film propertiesof the film thus formed, the 20° glossiness was measured. In the presentinvention, the higher 20° glossiness indicates that a more uniform filmis formed. The pencil hardness of the film was measured by means of acommercially available pencil hardness tester. These measured resultsare shown in Table 2. Incidentally, the pencil hardness test wasconducted according to the JIS standard. The higher pencil hardness inTable 2 indicates that a stronger film is formed.

Evaluation of Long-Term Storage Stability of Liquid Composition

Each of the liquid compositions of Examples 1 to 18 and ComparativeExamples 1 to 9 was placed in a closed container made of a fluororesinand stored for a month at 60° C. Conditions (viscosity and averageparticle size of pigment) of the liquid composition before and after thestorage were compared to conduct evaluation according to the followingcriteria. The evaluation results are shown in Table 2.

A: The conditions were not changed from the initial conditions evenafter the storage;

B: The viscosity and/or the average particle size was changed after thestorage.

TABLE 2 Evaluation results Film properties Long-term Film-formingability Pencil storage (20° glossiness) hardness stability Example 1 403H A Example 2 35 2H A Example 3 35 HB A Example 4 40 2H A Example 5 35H A Example 6 35 HB A Example 7 35 4H A Example 8 30 3H A Example 9 203H A Example 10 40 H A Example 11 40 F A Example 12 45 HB A Example 1343 HB A Example 14 45 H A Example 15 35 2H A Example 16 40 2H A Example17 15 3H A Example 18 40 4H A Comparative 30 2B B Example 1 Comparative30 2B B Example 2 Comparative (*6) 4B or less B Example 3 Comparative 404B or less A Example 4 Comparative 30 3B B Example 5 Comparative 30 2B BExample 6 Comparative (*6) 4B or less B Example 7 Comparative 40 4B orless A Example 8 Comparative 10 2B A Example 9 (*6) No film was formedunder the preparation conditions described above.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-250939, filed Oct. 30, 2009, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An ink jet recording method comprising: ejectinga liquid composition on a recording medium, the liquid compositioncomprising (a) a water-soluble monomer, (b) a photopolymerizationinitiator, (c) an aqueous medium, and (d) a polymer emulsion, whereinthe water-soluble monomer has two or more ethylenically unsaturatedbonds, wherein the water-soluble monomer is curable with an activeenergy ray, and wherein the liquid composition does not comprise acoloring material.
 2. The ink jet recording method according to claim 1,wherein the water-soluble monomer has a molecular structure satisfyingthe relationship of the following expression (1):3.5≦(Molecular weight of water-soluble monomer)/(28.05×(Number ofunsaturated double bonds in molecular structure))≦8.0.  Expression (1)3. The ink jet recording method according to claim 1, wherein thewater-soluble monomer has at least one hydroxyl group.
 4. The ink jetrecording method according to claim 1, wherein the photopolymerizationinitiator is a water-soluble acylphosphine oxide compound.
 5. The inkjet recording method according to claim 1, wherein the polymer emulsionis a water-insoluble polymer present in a state of an emulsion in theliquid composition.
 6. The ink jet recording method according to claim1, wherein the water-soluble monomer is at least one selected from thegroup consisting of the following Exemplified Compounds 1 to 9,


7. The ink jet recording method according to claim 1, further comprisingirradiating the recording medium on which the liquid composition hasbeen ejected with an active energy ray to cure the water-solublemonomer.
 8. The ink jet recording method according to claim 7, whereinthe active energy ray is an ultraviolet ray.
 9. The ink jet recordingmethod according to claim 1, wherein the polymer emulsion is a vinylchloride-acrylic ester copolymer, wherein the water-soluble monomer isthe following Exemplified Compound 7, and wherein thephotopolymerization initiator is the following Exemplified Compound A,


10. The ink jet recording method according to claim 1, wherein thephotopolymerization initiator is at least one selected from the groupconsisting of the compounds represented by the following GeneralFormulae (1), (3), (4), and (5),